Compressive and racking performance of eccentrically aligned dou-gong connections

This paper presents an experimental study on the compressive and racking performance of eccentrically aligned dou-gong connections used in Chinese traditional timber structures. Four 1:3.4 scaled specimens were fabricated and tested with static compressive and cyclic lateral loading. The damage modes and load-displacement (or hysteresis) curves of the dou-gong connections as well as the influence of the composite action effect and vertical compression loading were discussed. It was found that the load-displacement curve of an eccentrically aligned dou-gong connection was nearly bilinear and the change of the vertical stiffness took place when the cap block cracked and loosened the lateral constraint on the overturning of the connection. The vertical initial compressive stiffness was nearly 70% of a concentrically aligned dou-gong connection according to a predictive formula established based on concentrically aligned dou-gong connection test results. The initial stiffness, yield load and maximum load of double dou-gong connections were found to be 262%, 332% and 373% of those of a single dou-gong connection, respectively. The composite action from the interlocked straight beams (by shear keys) and infill panel can increase the lateral stiffness by more than 55% and the energy dissipation capacity by more than 70%, though such composite action decreases with the worn out of the contact surfaces of the straight beams and the plastic deformation of the shear keys. The vertical load improved the stiffness and energy dissipation capacity of the connections mostly by the friction force. Specifically, an increase of 120% in the vertical compression load can lead to more than 50% increase in the lateral stiffness and up to 130% increase in the energy dissipation capacity.